Water-base paint, the solvent of which consists mainly of water, has the drawbacks that it is slow to evaporate, has a strong surface tension, permits only a narrow latitude for solvent composition; and it is liable to develop the following paint defects, especially at high humidities (of over 70% relative humidity).
Major defects likely to occur are
(1) The applied paint may run down under the influence of gravity while the film is still wet and fluid.
(2) The applied paint may concentrate at a sharp bend in the object to be painted or the paint applied to other parts may run down and collect at such a sharp bend.
(3) The solvent may suddenly evaporate or a bubble therein may break where the film is thick due to collection of applied paint.
(4) The paint may be irregularly distributed when metallic paint is used.
(5) The metal in the paint may be attracted to a sharp bend in the object to be painted while a wet metallic paint is fluid and its surface tension is strong.
(6) The applied paint may form a "picture frame", when attracted to the edges of the object to be painted while the wet paint is fluid and the surface tension is strong.
Water-base paint here should be understood to include water emulsion paints, the water-dispersion paints and water-soluble paints.